This is the Microsoft Reserved Partition. Usually it's only 16MB in size but sometimes Windows makes it larger, or Seagate may have created it that size. (You formatted the main partition, but you didn't completely wipe the drive so the MSR partition wasn't removed.) This is a required partition when Windows creates a GPT drive, and is used for "partition management", even though other OSes get by fine without it. Windows's own tools will not display it because they don't want you to be able to delete it, but third-party tools will show it.
Seagate and other makers don't create hidden boot partitions on their drives. If they include tools like encryption stuff, they put it on the main partition that is visible to the user so they can install the software.
So don't do anything with it, but don't worry about it.